Many of electronic devices such as SAW filters, FBAR filters, and quartz oscillators are supplied in a mode of a package that is air-tightly sealed for protection of an element function part. A general configuration of this sealed package is such that a sealing structure is formed by covering a base, on which the element is mounted and fixed, with a cap serving as a lid.
In many cases, the shapes of the base and the cap of the sealed package are such that a cap having a flat plate shape is combined with a container-shaped base having a cavity. Conversely, there is also recently reported a structure in which a cavity is formed in a cap; an element is fixed to a base having a flat plate shape; and the cap is bonded to the base. This configuration in which a cavity is formed in a cap is a mode that is attracting people's attention in recent years because the configuration can contribute to cost reduction of the device by making the process of fixing the element to the base be efficient.
In bonding between the cap and the base, using a brazing material is effective for ensuring air-tightness in the inside of the package. As this brazing material, an Au-based brazing material (for example, Au—Sn-based brazing material) is often used from the reasons such as reliability and corrosion resistance. In package sealing to which a brazing material is applied, the brazing material is fused and fixed onto the cap in advance; the base is covered with the cap when the sealing work is performed; and the brazing material is melted again for bonding. FIG. 1 is a view for describing a step of producing a package to which a cap and a base are applied.
FIG. 2 is a view for describing a step of fusing and fixing the brazing material onto the cap before sealing the package. In both of a flat plate cap and a cap with a cavity, a brazing material-fused surface is set with a specification of the package taken into consideration. Typically, in the case of a flat plate cap, a brazing material-fused surface having a frame shape is set along the four sides of the cap (FIG. 2(a)). In a cap with a cavity, a brazing material-fused surface having a frame shape is set on the end surface of the cap (FIG. 2(b)). In the cap with a cavity, the end surface of a cap body that forms the cavity is bent to form a flange part having a brim shape, and this flange surface is set as the brazing material-fused surface.
A frame-shaped brazing material (Au-based brazing material) is fused and fixed onto these brazing material-fused surfaces; however, before that, Au plating is typically applied on the surface of the cap. This is in consideration of the material of the cap (where kovar (Fe—Ni—Co-based alloy), 42 alloy (Fe—Ni-based alloy), or the like is used). In other words, a molten Au-based brazing material has a poor wettability and hence raises a possibility that the frame shape may be collapsed when the brazing material is melted, so that Au plating is applied for ensuring the wettability on the surface of the cap. Also, for preventing oxidation of kovar, Ni plating may be applied before the Au plating. Further, the brazing material is fused after the plating process is performed in this manner.
In the meantime, a matter that must be paid attention to in performing the package sealing with use of the sealing cap prepared in the above-described manner is suppression of the flowing of the brazing material into the sealed region. At the time of sealing, the brazing material is melted again, and during that time, the brazing material may possibly be wet-spread and flow onto the surface of the base on which an element is to be mounted. The situation in which the brazing material flows onto the surface of the base to be brought into contact with the element is not preferable because this may lead to damages of the element.
A sealing cap prepared with the wet-spreading of the brazing material in sealing in mind may be, for example, a cap (lid) disclosed in Patent Document 1. This cap relates to a flat plate cap, which is produced through Ni plating and Au plating, putting a cap having a fused frame-shaped brazing material into a container together with a polishing medium, and swinging the container to perform polishing. By this polishing, almost all of the Au plating on the inside of cap is peeled off, and the remaining slight amount of Au is turned into an alloy together with the Ni plating. Since the Au-based brazing material has a poor wettability to Ni alloy, the flowing and spreading of the brazing material can be controlled.